Method for making cyclic esters



aamirmzcmac a g UNITED-STATES PATENTOFFIICE. f

vLII'ITHOD FOR- MAKING GYCLIC ESTEBS I Wallace Hume Carothcrs, Arden, and Julian f Werner Hill, Wilmington, Del., assignors to'E. I. du'l'ont de Nemours & Company, Wilmington, Del., a corporation oi. Delaware No Drawing. Application December 12, 1933,

- Serlal'No. 701,980 I v 9 Claims. (Cl. 260-338) This invention relates to the preparation of Among the specific compounds maybe mentioned cyclic esters having more than seven atoms in the xylene,- toluene, the product sold commercially ring. More specifically it relates to a method of as Hi-flash naphtha, chlorobenzene, .p,p-diincreasing the yield of these esters by suppressing chlordiethyl ether, acetylene tetrachloride, cyclothe formation of undesirable compounds. I hexanone and dibutyl ether. In this method of It is well known that cyclic esters having more establishing the ester linkage by direct esteriflthan seven atoms in the ring, such as, for examcation of a carboxyl group by a hydroxyl group, pie, the lactone oi w-hydroxypentadecanoic acid, the boiling point of the solvent should be in gencannot be obtained by the ordinary methods for eral above 100 0., although this is by no means 10 preparing five or six membered lactones. These necessary and the'unfavorable effect of a lower 10 higher cyclic esters have hitherto beenprepared boiling point may, of course, be eliminated'by the only by very laborious and complicated methods application of pressure. It is desirable to use a and the yields have been small. water-immiscible solvent so that water of reac- Applicants,in their copending application, Setion can be readily removed. This is accoml5 rial No. 657,408, filed February 18, 1933, now plished by distilling off water and solvent, sepavl5 U. 8. Patent 2,020,298, have described a method of rating the water, and returning the solvent conpreparing many-membered cyclic esters by deinuously to the reaction vessel.

polymerizing linear polyesters. The various reactions described herein may be It is an object of this invention to provide a carried out at widely varying temperatures, the

process of preparing cyclic esters having more only limits being that the temperature must be 20 than sevenatoms in the ring. It is a further obhigh enough to cause reaction but. not so high as ject of this invention to provide a simple and dlto bring about decomposition of the reactants rect method' of preparing thesevesters whichwill or reaction products. It .has been found that also result in higher yields. Other objects will the reaction can be very conveniently carried out appear hereinafter. in many cases at the boiling point of water, since 25 These objects may be accomplished by bringing any water of reaction must be removed. Cerabout the cyclic ester formation in the presence, tain solvents form with water binaries, boiling of an inert liquid at high dilution. The inert liqbelow the boiling temperature of water, and in mid should be a solvent for the reacting material, such cases the reaction temperature can be conor materials, veniently maintained at the boiling temperature 30 Example of the binary. x g It is highly desirable in carrying out the direct One P Of y oxyp c acid is esteriflcation to have present an esteriflcation dissolved in 1000 parts of dry xylene containing catalyst, and for this purpose a mineral acid,

5 a y small amount (about 1 of one part) oi such as sulfuric, phosphoric, hydrochloric, etc., 86-

p-tollleneslilfonic acid to c as a catalyst for or a strong organic acid, such as benzenesulionic, esteriflcation. The solution is heated to boiling p-toluenesulfonic, cainphorsulfonic, or naphthaunder a reflux condenser for a period of one hour lene sulfonic, may be-used.

or more and the xylene together with any water In the application of this process it is necessary f rm is h w y distilled h h a columnto have present a suiliciently high ratio oi'sol- 40 The residual material is found to contain the 18-0- vent acting as a diluent to depress considerably tone Of w-hy yp acid, which is the velocity 01' intermolecular reaction which easily recognized on account of its very intense brings about the formation [of undesirable byand highly characteristic odor. products. The minimum practical ratio of sol- In carry ng Out the process of the present invent to reacting compound will vary considerably vention any indifierent solvent having a suffl- .with the nature of the latter, but in general no ciently high boiling point may be used. By an important eflect of the solvent will be obtained indlil'erent solvent inthis connection we mean a unless its amount is at least twenty times greater qui which is n readily callable of being esterithan that of the reacting compounds. In genfled and does not hydrolyze or react with the eral it. is preferable to use at least one hundred 50 ester product to an important extent under the times as much of the solvent as of the reacting conditions used. As examples of such compounds compounds andas indicated in the example we may mention aromatic and aliphatic hydromuch greater amounts-even than this will be used carbons, aromatic and aliphatic ethers, ketones, at times.

and aromatic and aliphatic halogen compounds. The method oi this invention is applicable not 5' only to the synthesis of lactone of w-hydrompemfor the synthesis of cyclic-esters derived jointly from dibasic acids and dihydric alcohols. Asan example of such an ester we may mention cyclic monomeric ethylene sebacatehaving the formula:

which is described in the co-pending application of Carothers and Hill, referred to above. When 'sebacic acid and ethylene glycol are heated together reaction occurs-and an ester having the same mass formula as that above results. However, this product is a polyester and not the cyclic monomeric ester described above. According to the processof the present invention, if the ethylene glycol. and sebacic acid areallowed to react at low concentration in the presence of a large excess'of an inert diluent, the course of the reaction is changed in such a way that the desired cyclic ester tends to be formed instead of the.

polyester. This method may also be applied to other esters derived jointly from dibasic acids and dihydric alcohols, such as those derived from the acids oxalic, malonic, succinic, glutaric, adipicp suberic, pimelic, azelaic, bras'sylic, and tetradeca methylenedicarboxylic, and from the glycols,. ethylene glycol, propylene glycol, butylene glycol, trimethylene glycol, tetramethylene glycol, pen} tamethylene glycol, hexamethylene glycol, heptamethylene glycol, octamethyleneglycol, nonamethylene glycol, decamethylene glycol, undecamethylene glycol, dodecamethylene glycol, tridecamethylene glycol, tetradecamethylene glycol, diethylene glycol, triethylene glycol, etc.

The process of theinvention may also be extended to the preparation of many-membered cyclic esters by reactions other than direct esterification, and for this-purpose it is essential only that all the reactants be of such a nature that they can be simultaneously dissolved in an inert diluent. It is, for example, possible to obtain ethylene sebacate by the action of diphenyl sebacate on ethylene glycol. The reaction in this case consists in ester interchange rather than esterification, phenol instead of water being eliminated as thesecond reaction product. If the diphenyl sebacate is placed in an inert solvent at very low concentration together with an equiva-- lent amount of ethylene glycol this ester interchange will-proceed in such a manner as to yield a predominating amount of the monomeric cyclic ester, the formation of polyester being suppressed by the presence of the diluent.

The method of the present invention may also be applied to the synthesis of cyclic esters from a glycol and dibasic acid halide. In such cases, tertiary amines are desirable as catalysts. For example, a. l-molar solution of phosgene (acid chloride of carbonic acid) in toluene and a 1 molar solution of decamethylene glycol in pyridine are added separately and simultaneously at a very slow andexactly equal rate to a reaction CH3CaH4SO3-(CH2) isCOOM or Br(CHz)-15COOM, where M is a metal, may' be caused to react with itself in high dilution. The latter reaction should be carried out in a medium capable of dissolving the salt. As a still furthermethod, a derivative of a glycol such as the di-p-toluenesulfonic ester 'cqmsouonnxsoicqm may be caused to act on a salt of a dibasic acid. X.in the foregoing formula has aminimum value 'of two to four, depending on the acid, and has no set maximum value. In cases of this kind it is possible-to use even-such reactive solvents as'water for the reacting medium and to carry. out the reaction at a temperature considerably below C.

" The many-membered cyclic esters are in many cases odorous compounds of great value. Many of them such as the lactoneof w-hydroxypentadecanoic acid, tetradecamethylene carbonate, and ethylene sebacate have odors closely resembling those of natural musk. At the same time they possess the extraordinary fixative power which is characteristic of natural musk but is absent from most synthetic musks. The present invention provides-a simple and direct method, for their preparation. By the .process of this invention it'is possible also to obtain high yields of a pure product. In addition the method herein described may be applied to a wide variety of syntheses. Other advantages will be apparent from the above description and specific example.

The term radical length, as used herein and in the claimsto characterize the reactants, in-

dicates those atoms in the chains of the glycol,

dicarboxylic acid, hydroxy acid, or ester-forming deriyative thereof, as the case may be, which become annular' atoms in the cyclic ester produced. Thus the radical length of a glycol is equal to the number of atoms in the chains between the hydroxyl groups,-p lus the two hydroxyl oxygen atoms; that of a dicarboxylic acid is the numberof atoms in the chains between the carboxyl groups, plus the two carboxyl carbons; and that of a hydroxy acid is the number 'of atoms in the chains between the carboxyl and hydroxyl groups, plus the carboxyl carbon and the hydroxyl oxygen. Carbonic acid has a radical length of one.

' It is apparent that many widely diiferent embodiments of this invention may be made withoutdeparting from the spirit and scope thereof, therefore, it is'not to be' limited except as indicated in the appended claims.

We claim:

1. The process of preparing the lactone of whydroxypentadecanoic acid which comprises boiling a mixture of one part of w-hydroxypentadecanoic acid in at least 1,000 parts of'dry xylene,

to which has been added .01 of one part of para toluenesulfonic acid, for at least 60 minutes and then slowly distilling off the xylene and water of reaction.

2. A methodof preparing -cyclic monomeric ethylene sebacate which comprises reacting ethylene glycol and sebacic acid in the presence of a large amount of an inert liquid which is a solvent for the reactants.

and the hydroxyl groups of the alcohol is at least 3. The process of claim 2, characterized in that the inert solvent is xylene. 4. A process which comprises heating aliphatic ester-forming substances of such character as to give cyclic esters having more than seven annular atoms in the presence of an at least one hundred-fold quantity of an inert organic liquid which is a solvent for the reacting material.

5. A process which comprises heating an aliphatic monohydroxy monocarboxylic acid having at least six atoms in the chain between the hydroxyl and the carboxyl groups in the presence of an at least one thousand-fold quantity of an inert organic liquid which is a solvent for the hydroxy acid.

6. A process which comprises heating an aliphatic dicarboxylic acid and an aliphatic'dihydric alcohol so selected that the sum oilthe atoms in the chain between the carboxyl groups of the acid four, in the presence of an at least one thousandfold quantity of an organic liquid which is a solvent for said acid and-alcohol.

7. The process according to claim 4 in which the reaction is carried out in the presence of a mineral acid.

8. The process according to claim 4 in which the reaction is carried out in the presence of a strong organic acid.

9. A process which comprises heating-aliphatic ester-forming substances of such character as to give cyclic esters having more than ten annular I atoms in the presence of an at least one hundredfold quantity of an inert organic liquid which is a solvent for the reacting material.

WALLACE H. CAROTHERS. JULIAN W. HILL. 

